Dermal Wound Healing Process
Dermal wound healing is a complex process that, when properly orchestrated, leads to reestablishment of skin integrity with minimal residual scarring. Normal wound healing includes a transition from a proliferative phase, during which extracellular matrix (ECM) proteins are elaborated, to a remodeling phase, during which the wound is strengthened through stromal organization. Abnormal wound healing may result in pathologic dermal scarring, which represents a diverse spectrum of disorders that range from unsightly scars, to keloids, to life-threatening systemic diseases such as scleroderma. One example of pathologic dermal scarring is hypertrophic scars that are an unfavorable outcome of burns, trauma, or surgery. Although much has been learned about the pathophysiology of pathologic dermal scarring, most treatment modalities lack a defined mechanism of action, are non-specific, and have limited efficacy (Mustoe 2004). Indeed to date, there are no FDA approved drugs to treat dermal scarring.
The Roles of Transforming Growth Factor-Beta (TGF-β) and Connective Tissue Growth Factor (CTGF)
There is widespread evidence that dysregulation of the transforming growth factor-beta (TGF-β) family leads to scarring in a variety of chronic inflammatory conditions and in response to acute injury. (Shah et al. 1995; Leask and Abraham 2004) As such, TGF-β has been the target of many therapeutic approaches designed to limit acute and chronic fibrosis. However, since TGF-β plays pleiotrophic physiologic roles, efforts to modulate it have been limited by concerns about treatment specificity. (Shull et al. 1992) For example, neutralization of TGF-β reduces fibrosis in animal models of surgical scarring (Lu et al. 2005; Shah et al. 1992) but has also delayed wound healing. (Sisco et al. 2005)
Another growth factor of interest is connective tissue growth factor (CTGF), which is a matricellular protein that is known to regulate aspects of cell proliferation, migration, differentiation, angiogenesis, ECM production, and adhesion. (Frazier et al. 1996) Overexpression of CTGF mRNA and protein has been observed in chronic fibrotic disorders affecting multiple organ systems. In the skin, the role of CTGF in fibrosis is becoming better defined. Although CTGF has minimal basal expression in normal skin, it demonstrates transient up-regulation for several days following dermal injury. (Lin et al, 2005; Igarashi et al. 1993; Dammeier et al. 1998) In contrast, persistent overexpression of CTGF has been observed in biopsies of keloids and localized sclerosis. (Igarashi et al. 1996) Fibroblasts cultured from hypertrophic scars, keloids, and scleroderma lesions express increased basal CTGF. (Colwell et al. 2006; Shi-Wen et al. 2000) In addition, cells cultured from hypertrophic scars elaborate more CTGF in response to stimulation with TGF-β. (Colwell et al. 2005)
Since TGF-β potently induces CTGF through several pathways, CTGF has long been thought to mediate many of its fibrotic effects. Indeed, studies in various cell populations have demonstrated roles for CTGF in the TGF-β-dependent induction of fibronectin (Fn), collagen, and tissue inhibitor of metalloproteinase-1 (TIMP-1). (Frazier et al. 1996; Blalock et al. 2003; Grotendorst 1997; Wang et al. 2004) A more recent paradigm suggests that CTGF functions as a co-factor to TGF-β by enhancing ligand-receptor binding in activated cells. (Abreu et al. 2002) This may explain research that shows a limited ability of CTGF to induce ECM production and sustained fibrosis in vivo in the absence of TGF-β. (Frazier et al. 1996; Bonniaud et al. 2003; Mori et al. 1999) In addition, while CTGF mediates the effects of TGF-β on myofibroblast differentiation, it is insufficient to bring about this change when introduced exogenously (Folger et al. 2001).
There are several examples whereby TGF-β-independent induction of CTGF may contribute to its pathologic activity. Mechanical stress induces CTGF expression directly (Garrett 2004; Kessler et al. 2001; Schild et al. 2002). Elevated expression of CTGF, without a concomitant rise in TGF-β, has been observed in response to several factors known to contribute to healing, such as thrombin, factor VIIa, and exogenous CTGF. Furthermore, endothelin-1, epidermal growth factor, fibroblast growth factor, vascular endothelial growth factor, and platelet-derived growth factor can independently initiate transcription of CTGF in fibroblasts.
CTGF may be an attractive target for modulating hypertrophic scarring for several reasons. As a cofactor and downstream mediator of TGF-β, CTGF may represent a more specific target than TGF-β for gene-directed molecular therapies aimed at scarring, particularly since TGF-β has pluripotent effects unrelated to scar formation. In addition, CTGF may have TGF-β independent functions in maintaining a fibrotic phenotype that would be neglected by anti-TGF-β strategies. Despite advances in understanding CTGF's roles in augmenting fibrosis in multiple organ systems and in chronic dermal diseases such as scleroderma, CTGF's roles in acute scarring and wound healing remain largely observational.
To determine whether CTGF was necessary for wound healing and scar hypertrophy, a study was conducted whereby CTGF was specifically blocked in well-characterized rabbit models. The goal of the study was also to determine mechanisms whereby CTGF might be exerting its effect. The hypothesis was that inhibition of CTGF expression in vivo would abrogate fibrosis without having a detrimental effect on wound closure, a finding that has not been previously shown in skin by others.
The Role of Antisense Oligonucleotide
Antisense technology is an effective means for reducing the expression of specific gene products and may be uniquely useful in a number of therapeutic, diagnosic, and research applications for the modulation of connective tissue factor expression. (Garde et al., 2005, U.S. Pat. No. 6,965,025B2)
An antisense compound is an oligomeric compound that is capable of undergoing hybridization to a target nucleic acid (e.g. target mRNA).
Antisense compounds, compositions and methods for modulating expression of connective tissue growth factor and for treatment of disease associated with expression of connective tissue growth factor are disclosed intra alia in U.S. Pat. No. 6,965,025B2.